Antiperspirant emulsion sticks are solidified compositions characterized as having aqueous and oil phases. Among such antiperspirant emulsion sticks are compositions having a disperse aqueous phase in which is dissolved antiperspirant active, commonly aluminium, zirconium and/or mixed aluminium/zirconium salts, and a continuous oil phase comprising one or more gelling agents capable of structuring such phase.
Antiperspirant emulsion sticks can be formulated as clear (i.e., translucent or transparent) or opaque compositions. Translucent or transparent emulsion sticks go on clear and, depending upon their formulation, may remain clear for extended periods of time, reducing the consumer perceived negative of “white marks” associated with deposition of antiperspirant active.
In antiperspirant emulsion sticks, clarity of the stick itself is commonly achieved through a combination of technology approaches. Solidifying the emulsion with a structurant that has a very fine and homogeneous microstructure provides a stick in which light scattering is minimized. Emulsion sticks in which the oil phase is structured with a fiber-forming amido gelator and a liquid fatty alcohol represent a class of sticks having relatively fine and homogeneous microstructures. Such emulsion sticks are described, for example, in U.S. Pat. Nos. 6,241,976 and 7,347,990. The extent to which an emulsion's aqueous and oil phases are matched is another factor that impacts stick clarity.
On a production scale, there are a number of significant challenges to achieving RI matching of the aqueous and oil phases, including lot-to lot variability in the refractive indices of raw materials, principally the antiperspirant active. As a practical matter, adjusting the emulsion to a fixed RI for all batches is not trivial and tends to be done by trial and error. While the refractive index of the aqueous phase varies with active concentration, the variation typically does not follow a linear progression. Moreover, to achieve optimum sensory properties, the water content in proportion to active is relatively fixed, i.e., water is typically present in an amount sufficient for the active to be dissolved without giving rise to a formulation that is “wet” or “sticky”. Accordingly, it is generally more desirable to modify the oil phase to match the refractive index of the aqueous phase, rather than modifying the refractive index of the aqueous phase to match that of the oil phase.
While the oil phase offers more flexibility in terms of refractive index matching, it too has constraints, one such constraint being the need to solubilize the gelator (herein also referred to as the gelling agent or gellant) during stick preparation. Liquid fatty alcohols such as, for example, isostearyl alcohol and octyl dodecanol are known to be especially effective in solubilizing amido gelators. While desirable for their solubility properties, owing to their heavy, oily feel, liquid fatty alcohols tend to detract from sensory properties. To optimize sensory properties, it is generally desirable to minimize the amount of liquid fatty alcohol, and to further include in the oil phase a relatively high level of oil with better sensory properties. Typically such oil includes volatile oil, in particular, volatile silicone oil.
The volatile silicone oil of choice is commonly cyclomethicone. Cyclomethicone is nominally designated as D4, D5 or D6, depending upon the particular cyclomethicone (e.g., cyclotetrasiloxane, cyclopentasiloxane or cyclohexasiloxane) predominant therein. Cyclomethicone is compatible with numerous carrier oils as well as with amido gelators and emulsifiers, in particular, the silicone based emulsifiers commonly employed in such compositions. Volatile silicone oils are generally considered to impart good sensory feel to such formulations, i.e., a clean, dry feel. Additionally, the surface tension and spreadability of cyclomethicone can contribute to the emulsion sticks in which they are used having a smooth or silky feel on application.
Volatile linear polydimethylsiloxanes, often referred to as volatile dimethicones, such as, for example, those sold by Dow Corning with the names DC200 Fluid 1 cst and DC200 Fluid 5 cst, are in some cases used as complete or partial alternatives to the cyclomethicones. Non-silicone volatile oils may also be employed for similar sensory purposes. These include linear and branched hydrocarbons containing less than about 16 carbon atoms.
Volatile oil may, however, evaporate during stick production thereby contributing to mismatching of the refractive index of the oil and aqueous phases which, in turn, can lead to stick clarity being compromised. In addition to volatile oil potentially contributing to RI mismatch, its use may complicate emulsion stick production, particularly if the processing temperature of the amido gelator exceeds the flash point of the volatile oil.
As well as offering potential processing advantages, minimizing volatile oil content may be desirable from an environmental or regulatory perspective.
It is an aspect of the present invention to provide an antiperspirant emulsion stick that overcomes or ameliorates one or more of the issues disclosed above. More particularly, one aspect of this invention is to provide an emulsion stick that includes an amido gelator and a solvent fatty alcohol, in which composition the RI of the aqueous and oil phases are relatively easily matched. Another aspect of this invention is to minimize or virtually eliminate volatile silicone oil and other volatile oils (exclusive of perfume oil), while providing a stick that retains desirable clarity and sensory feel. In one or more embodiments, another aspect of this invention is to virtually eliminate silicone oil in an antiperspirant emulsion stick while retaining the ability to use a silicone based emulsifier therein.